Flight endurance of unmanned air systems is limited by an amount of energy that can be stored on board. For an electrically powered UAS this is limited by an amount of charge that can be stored in a battery and its state of charge, or for a fuel cell powered UAS this is limited by an amount of fuel for feeding a fuel cell that can be carried. Batteries are heavy. Hydrogen is commonly used as a fuel for feeding fuel cells but hydrogen is a very light molecule which is difficult to store without heavy containment vessels. Considerable amounts of hydrogen are also required for extended flight durations.